The present invention relates to a device for studying physical properties of solid samples in the presence of fluids, at high temperature and pressure.
The device according to the invention is suited for testing for example geologic samples and for determining various parameters such as the capillary pressure of rocks in drainage or imbibition phases, their wettability index, their relative permeability, their resistivity index, etc, under temperature and pressure conditions reproducing those found in reservoirs containing or likely to contain hydrocarbons and from which they are taken.
In order to determine the distribution of the oil and gas volumes in a reservoir, the values of the saturations that depend on parameters such as the wettability and the interfacial tension have to be known at any point. The wettability of rocks with regard to the water and to the oil that may be contained therein is therefore determined. The rock must therefore be subjected to drainage operations, i.e. displacement of the fluids in order to decrease the water saturation, followed by imbibition operations, this term referring to displacement of the fluids allowing to increase the water saturation (Sw) of the rock. The capillary pressure at one point of a porous material containing two fluids such as water and oil in the continuous phase is defined, as it is well-known, as the difference Pc at equilibrium between the pressure P(oil) of the oil and the pressure P(water) of the water.
Knowledge of various parameters and notably of the wettability of the rocks is useful notably when enhanced recovery is to be performed in a formation, by draining the effluents contained therein by injection of a fluid under pressure, and when the most suitable fluid (water or gas) for effluent displacement is to be selected by means of preliminary tests.
Various types of devices are used to carry out these drainage and imbibition operations in the laboratory. The sample bars are generally placed in a cell. At the opposite ends thereof, the cell comprises two end pieces communicating with means intended to establish displacement of fluids under pressure through the sample tested. Measuring means are used to measure various parameters pressures, saturations, electric resistivity, etc. The sample bar can be placed inside an elastomer containment vessel compressed by injection of fluid under pressure.
Various devices for measuring physical parameters of porous solid samples are described for example in patents FR-2,708,742, FR-2,724,460 (U.S. Pat. No. 5,610,525) or FR-2,728,684 (U.S. Pat. No. 5,637,796) filed by the applicant.
Monitoring of the displacement of the fluids in a sample is often performed by using X-ray or gamma-ray investigation means exterior to the cell. The walls of the cell body must be sufficiently resistant to withstand confining pressures of several ten MPa while remaining transparent to the radiation and therefore relatively thin.
Conventional means for maintaining the sample at a relatively high temperature (150xc2x0 C. for example) : drying oven or heating jackets wound around the body, are hardly compatible with the use of a radiation investigation device because they are interposed between the latter and the sample, and they contribute still further to radiation attenuation.
The device according to the invention allows to measure physical properties of a sample at relatively high pressure and temperature, while avoiding notably the drawbacks of the prior art.
The device comprises an elongate rigid body closed at the opposite ends thereof by two end pieces, a flexible sheath around the sample, cooperating with the two end pieces so as to delimit a containment vessel inside the rigid body, means for establishing displacement of fluids under pressure through the sample in its vessel, means for measuring various parameters of the sample and means for injecting a fluid under pressure around the flexible sheath so as to exert a radial pressure around the sample.
The device comprises means for heating the fluid under pressure (such as electric resistors) associated with at least one of the two covers and means for homogenizing the temperature around the sheath by circulation of the fluid heated on contact with the heating means.
The fluid circulation means comprise for example a stirring means cooperating with a circuit intended to circulate the fluid in contact with the heating means.
According to an embodiment, the stirring means comprises a turbine driven by a motor, that is placed in a cavity of one of the two covers, and the circuit intended for circulation of the fluid in contact with the heating means comprises a tube placed in the annular space between the body and the sheath, this tube communicating lines interior to the two covers.
According to a preferred embodiment, the body comprises a tubular part made of a composite material, the two covers being made of a good heat-conducting material.
The covers can be secured to the body either directly or by means of ties that can also be made of a composite material.
The device comprises for example channels provided through the two covers for communicating the ends of the sample with fluid circulation means.
The measuring means can comprise a device for measuring the absorption of a radiation by said sample.
The heating mode used is advantageous because it is simple and effective. The heating means are in direct contact with the sample, which allows to reduce the time required for uniform temperature distribution. Furthermore, no exterior element likely to absorb radiations emitted by measuring devices exterior to the body is interposed, the radiation measuring sensitivity being thus improved.
Using a body made of a composite material also allows to limit the required thickness compatible with the high pressures necessary for measuring operations. The low absorption of radiations emitted by the measuring devices exhibited by such a material furthermore allows to facilitate the implementation thereof.